Sensorless Control of Ultrahigh-Speed PM Brushless Motor Using PLL and Third Harmonic Back EMF

1. Sensorless Control of Ultrahigh-Speed PM BrushlessMotor Using PLL and Third Harmonic Back EMF Student: yi-sin Tang Adviser: Ming-Shyan Wang Date : 2008.12.15 J. X. Shen, Senior Member, IEEE, and S. Iwasaki, IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 53, NO. 2, APRIL 2006

2. Outline • Abstract • 1. Introduction • 2. Orignal sensorless control • 3. Improved sensorless control • 4. Experimental invertstigation • 5. Conclusion

3. Abstract • Application-specific integrated circuit (ASIC)ML4425 is often used for sensorless control of permanent-magnet (PM) brushless direct current (BLDC) motor drives. 2. Basic principle and implementation of the new ASIC- based sensorless controller will be presented, and expermental results will be given to verify the control strategy. 3. The paper also uses the integration of third harmonic back EMF and the PLL technique and provides controllable advanced commutation to the BLDC motor.

4. Introduction • There are many categories of sensorless control strategies; however, the most popular category is based on back electromotive forces (EMFs). Basically, the EMFs can be utilized in three ways: 1. Detecting the EMF zero crossings. 2. Integrating the EMF from its zero crossing and comparing the integration result with a reference voltage. 3. Integrating the EMF and using a phase-locked loop (PLL) to keep the integration result being zero.

5. Introduction 1. ML4425 is often used for sensorless control of BLDC drives.It integrates the terminal voltage of the unenergized winding that contains the phase EMF information 2. PLL ensures that the integration result be zero. Thus, the BLDC motor can be commutated with a proper frequency and phase angle. 3. In most cases, the ASIC provides very reliable operation, and its peripheral circuit is simple.

6. ML4425 • 1.Made by “Micro Linear” • Work Voltage:12V • Work Frequeny:1.5~2.2kHz • PWM Frequeny:28kHz • 2. Controller functions include： • （1）Start-up circuitry • （2）Back-EMF commutation control • （3）Pulse Width Modulation (PWM) speed control • （4）Current limiting

7. ML4425 Diagram

8. ML4425

9. ML4425

10. ORIGINAL SENSORLESS CONTROL Schematic diagram of BLDC drive. Signal connection in original controller.

11. ORIGINAL SENSORLESS CONTROL Principle of original controller without considering freewheel diode conduction.

12. ORIGINAL SENSORLESS CONTROL

13. IMPROVED SENSORLESS CONTROL

14. IMPROVED SENSORLESS CONTROL

15. IMPROVED SENSORLESS CONTROL

16. IMPROVED SENSORLESS CONTROL

17. IMPROVED SENSORLESS CONTROL Waveforms of phase back EMFs and third harmonic back EMF in experimental BLDC motor.

18. IMPROVED SENSORLESS CONTROL

19. EXPERIMENTAL INVESTIGATION • Waveforms of phase current (captured), • third harmonic back EMF(captured), and • phase back EMF (synthesized) when • BLDC motor is operated with original • sensorless controller. • 10 kr/min, 21.7 V dc, 1.18 A dc. • (b) 120 kr/min, 272.7 V dc,21.6 A dc.

20. EXPERIMENTAL INVESTIGATION Waveforms of phase current (captured), third harmonic back EMF(captured), and phase back EMF (synthesized) when BLDC motor is operated with improved sensorless controller. (a) 10 kr/min, 19.5 V dc, 1.14 A dc. (b) 120 kr/min, 261.7 V dc, 21.6 A dc.

21. CONCLUSION 1.In this paper, an improved ASICbased controller using the third harmonic back EMF instead of the terminal voltages has been developed. 2.Its principle and implementation are presented, and its enhanced performance is verified with experimental results. 3.The current phase delay due to the winding inductance influence can be eliminated; hence, the system performance would be further improved.

22. Thanks for your attention